The present invention relates to a mechanical seal assembly, and more particularly, to an improved mechanical seal assembly designed for installation in dynamic applications, wherein the rotating shaft experiences substantial axial vibrations.
Various mechanical seals have been designed to provide a seal between a rotating shaft and its housing to prevent leakage of fluid between the shaft and the housing. Generally, mechanical seal assemblies are an arrangement of rotating (R) and non-rotating (NR) sealing rings that are positioned about the rotating shaft and maintained in close contact by a biasing force. The sealing rings have flat seal faces that, when forced together, create an annular seal about the shaft. A typical mechanical seal assembly includes a single R sealing ring locked to the rotating shaft, forming the end of the seal, and a single movable, NR sealing ring adjacent to the rotating sealing ring. The biasing force is applied to the back face of the NR sealing ring, for example by means of a spring, to urge the sealing rings into close sealing contact. Alternatively, bellows may also be used to apply the biasing force, or it is further known to use a controlled pressurized fluid.
Many problems are associated with state-of-the-art mechanical seal designs. First, mechanical seals have a high level of complexity and numerous parts, resulting in frequent malfunction, disassembly, and repair. In designs employing springs, problems occur with non-uniform loading and the application of an insufficient biasing force due to wear between the contacting seal face surfaces of the sealing rings. It is also difficult to maintain the sealing rings in a concentric relationship relative to the shaft, resulting in misalignment between the parts that disrupts the sealing contact between the sealing rings.
Maintaining sealing rings in permanent contact is especially problematic in dynamic applications characterized by strong axial shaft vibrations. Simply increasing the biasing force to counter the disruptive axial vibrations may cause significant heat generation between the contacting surfaces, distortion of or cracks in the sealing rings, and ultimately, mechanical seal failure. Another response is to utilize the NR sealing ring as a mechanical diode, such that the NR sealing ring is restricted to axial movement in the direction of the R sealing ring only, by providing the NR sealing ring with a cylindrical extension from its back face that also encircles the shaft, disposing balls or other wedging elements between the outer surface of the cylindrical extension and an internal conical section of the housing, and using springs disposed between the balls and the NR sealing ring to apply a constant force to both the NR sealing ring and balls to provide sealing contact between the sealing rings, and to prevent any disconnection of the sealing rings. Unfortunately, adapting the NR sealing ring to function as a mechanical diode does not correct misalignment problems, with respect to the sealing rings about the shaft, or address the need for the mechanical seal assembly to be sensitive to axial displacement of the mechanical diode itself, such that disconnection of the sealing rings and undesirable leakage of fluid from the seal is identified as early as possible and avoided.
A need in the art exists for a mechanical seal with reliable sealing contact between the sealing rings, especially in dynamic applications where the shaft and mechanical seal assembly are subjected to substantial axial vibrations (e.g., bore-hole drilling equipment).
The present invention is an improved mechanical seal assembly that includes a mechanical diode element, separate from the sealing rings, and also incorporates a hemispherical joint into the design of the mechanical diode for connecting the mechanical diode to a NR sealing ring. Significantly, the hemispherical joint allows for self-adjustment of the NR sealing ring about the shaft to ensure sufficient sealing contact between the NR and R sealing rings. A series of linear bearings are positioned axially adjacent to the mechanical diode for maintaining the alignment of the mechanical diode with the shaft and housing. An annular mechanical seal assembly housing may also be provided to contain the mechanical diode element, or a bellows connection may be used to contain the mechanical diode element, while also preventing rotation of the NR sealing ring and simplifying the mechanical seal assembly design.
In an alternate embodiment, the mechanical seal includes a mechanical amplifier of NR sealing ring axial movement comprised of a lever and connecting link, such that the mechanical diode readily identifies any axial movement of the NR sealing ring and prevents any disconnections of the sealing rings.
In yet another embodiment, the mechanical seal includes a hydraulic amplifier of NR sealing ring axial movement comprised of a pressurized fluid chamber, in combination with the NR sealing ring and the mechanical diode, such that the mechanical diode readily identifies any axial movement of the NR sealing rings and prevents any disconnections of the sealing rings.
Therefore, in view of the above, a basic object of the present invention is to provide an improved mechanical seal assembly that incorporates a hemispherical joint into a mechanical diode design to significantly increase the reliability of the mechanical seal, particularly in dynamic applications.
Another object of this invention is to provide an improved mechanical seal assembly having a NR sealing ring that is self-adjusting to provide good sealing contact with the R sealing ring, regardless of any misalignment between mechanical diode and the NR and R sealing rings.
Another object of this invention is to provide an improved mechanical seal assembly that affords early detection of any disconnection between the NR and R sealing rings.
Yet another object of this invention is to provide an improved mechanical seal assembly that prevents any disconnection between the NR and R sealing rings by means of a mechanical amplifier of NR sealing ring axial displacement.
Yet another object of this invention is to provide an improved mechanical seal assembly that prevents any disconnection between the non-rotating and rotating sealing rings by means of a hydraulic amplifier of NR sealing ring axial displacement.
A further object of this invention is to provide an improved mechanical seal assembly that increases the sensitivity of a mechanical diode component to axial displacement of the mechanical diode itself, such that the mechanical seal is significantly more reliable when subjected to axial vibrations of the shaft.
Additional objects, advantages, and novel features of the invention are set forth in the description below and/or will become apparent to those skilled in the art upon examination of the description below and/or by practice of the invention. The objects, advantages, and novel features of the invention may be realized and attained by means of instrumentation and combinations particularly pointed out in the appended claims.
Briefly, this invention is an improved mechanical seal assembly that provides a reliable seal between a rotating shaft and its housing by incorporating a hemispherical joint between a mechanical diode and a non-rotating (NR) sealing ring. The mechanical diode generally includes a sleeve encircling and extending along a desired length of the rotating shaft and terminating in an annular joint member also encircling the shaft. The annular joint member has a concave, hemispherical radial surface that is shaped to fittingly receive a convex, hemispherical radial surface of a non-rotating sealing ring, thereby forming an annular hemispherical joint about the shaft. At least one spring acts upon the annular joint member of the mechanical diode, such that the NR sealing ring is maintained in reliable sealing contact with a rotating (R) sealing ring by the mechanical diode via the spherical joint. The combination of the mechanical diode with the annular hemispherical joint provides freedom to the NR sealing ring for self-adjustment and reliable contact between the NR and R sealing rings, regardless of any misalignment of the mechanical diode and the NR sealing ring.
Preferably, the alignment of the mechanical diode about the rotating shaft is maintained by a series of linear bearings positioned axially along the sleeve of the mechanical diode. For additional flexibility, a bellows connection may be provided between the housing and a NR sealing ring, such that the mechanical diode is disposed within the interior of the bellows.
In an alternative embodiment, the improved mechanical seal includes a mechanical amplifier for amplifying axial movement of the NR sealing ring. The mechanical amplifier is generally comprised of link and lever members for connecting the mechanical diode to the NR sealing ring, increasing the sensitivity of the mechanical diode to any axial displacement of the NR sealing ring away from the R sealing ring, as well as incidental axial displacement of the mechanical diode itself. The mechanical diode responds to limit the axial movement of the NR sealing ring, resulting in early detection and correction of any disconnections between the sealing rings.
In yet another embodiment, the improved mechanical seal assembly includes a hydraulic amplifier for amplifying axial movement of the NR sealing ring. Hydraulic amplification is accomplished using an annular fluid chamber, preferably filled with oil, in combination with the back face of the NR sealing ring and the sleeve of the mechanical diode. The fluid is displaced by axial motion of the NR sealing ring, for example, axial motion caused by shaft vibration, and the resulting displacement of fluid within is transferred to the mechanical diode, which stops the NR sealing ring axial movement at its earliest phase.